Sweden: Prehospital Lactate Levels in Seizure Diagnosis

Measuring prehospital lactate levels in blood can help in seizure diagnosis in cases of transient loss of consciousness, according to a recent study in the journal Epilepsia. The study finds that prehospital blood lactate levels ≥4.75 mmol/L are suggestive of seizure as the cause of transient loss of consciousness.

"The timing of a lactate test is important, and higher cut‐offs are needed for interpretation of values measured prehospital compared to hospital‐based ones," write the authors.

Blood concentration of lactate increases immediately after a tonic‐clonic seizure. This occurs as a consequence of muscle hypoxia during convulsions. Serial measurements have shown that lactate levels normalize within a few hours of seizure. Lactate is a marker of tissue hypoxia and the value of prehospital lactate measurement in blood is currently explored in a range of conditions such as trauma or sepsis.

The use of blood lactate levels for the diagnosis of seizures in acute settings has been debatable. Johan Zelano, Gothenburg University, Gothenburg, Sweden, and colleagues aimed to assess the value of prehospital measurement of lactate level in blood for diagnosis of seizures in cases of transient loss of consciousness.

For the purpose, the researchers measured prehospital lactate between March 2018 and September 2019, with a point‐of‐care device by the emergency medical services in an area serving a population of 900,000. The researchers identified a total of 383 cases of transient loss of consciousness and categorized them as tonic‐clonic seizure (TCS), other seizure, syncope, or other cause (135 TCS, 42 other seizure, 163 syncope, and 43 other causes), according to the final diagnosis in the electronic medical records system.

Receiver operating characteristic curve analyses were used to identify the optimal lactate cut‐off.

Key Findings of the Study

• The median lactate level in TCS was 7.0 mmol/L, compared to a median of 2.0 mmol/L in all other cases.
• The area under the curve (AUC) of TCS vs nonepileptic causes was 0.87.
• The optimal cut‐off (Youden index, 67.8%) was 4.75 mmol/L, with 79% sensitivity and 89% specificity for TCS.

"Prehospital lactate can be a valuable tool for identifying seizures in transient loss of consciousness. For acceptable specificity, a higher cut‐off than that previously demonstrated for hospital‐based measurements must be used when values obtained close to the time of the event are interpreted," wrote the authors.

In simple words, prehospital lactate levels are useful for identifying seizures, but a higher cut‐off is needed than for hospital‐based measurements.

"Prehospital lactate levels in blood as a seizure biomarker: A multi‐center observational study," is published in the journal Epilepsia.

DOI: https://onlinelibrary.wiley.com/doi/10.1111/epi.16806